[FFmpeg-devel] [PATCH] avformat/movenc: fix VVC encoding with leading pictures

[Gabriel Hege <g+ffmpeg@hege.cc>]

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This is a resubmission with a corrected commit message.


The default behavior for VVenC (since v1.10.0) is to create an IDR with
leading pictures for the first picture in decoding order (POC 32). This
leads to FFmpeg generating an edit list with an empty entry, skipping
the leading pictures.

This patch fixes the calculation for the start_pts, while the DTS is
negative (as produced by libvvenc).


How to reproduce the issue (needs --enable-libvvenc and a recent 
libvvenc, e.g. v1.13):

Encode VVC directly into MP4 container:
./ffmpeg -i /data/YUV/foreman_352x288_30Hz_i420_8.y4m -an -preset faster 
-vcodec vvc test.mp4

   -> encodes 300 frames.

Decode to YUV (or play back using ffplay):
./ffmpeg -i test.mp4 test.yuv

   -> outputs 271 frames

When dumping the mp4-structure using 'MP4Box -diso test.mp4', I see the 
following EditListBox, which skips the first couple of 
frames:<EditListBox Size="40" Type="elst" Version="0" Flags="0" 
Specification="p12" Container="edts" EntryCount="2">
<EditListEntry Duration="1033" MediaTime="-1" MediaRate="1"/>
<EditListEntry Duration="8967" MediaTime="18432" MediaRate="1"/>
</EditListBox>


With the fix applied 300 frames are decoded as expected and the 
EditListBox looks like this:
<EditListBox Size="28" Type="elst" Version="0" Flags="0" 
Specification="p12" Container="edts" EntryCount="1">
<EditListEntry Duration="10000" MediaTime="2560" MediaRate="1"/>
</EditListBox>

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From d241417038ef78c1d2eb6c38e515a5153082a65f Mon Sep 17 00:00:00 2001
From: Gabriel Hege <g+ffmpeg@hege.cc>
Date: Wed, 16 Apr 2025 13:51:06 +0200
Subject: [PATCH] avformat/movenc: fix VVC encoding with leading pictures

The default behavior for VVenC (since v1.10.0) is to create an IDR with
leading pictures for the first picture in decoding order (POC 32). This
leads to FFmpeg generating an edit list with an empty entry, skipping
the leading pictures.

This patch fixes the calculation for the start_pts, while the DTS is
negative (as produced by vvenc).

Signed-off-by: Gabriel Hege <g+ffmpeg@hege.cc>
---
 libavformat/movenc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libavformat/movenc.c b/libavformat/movenc.c
index 4bc8bd1b2a..305f920022 100644
--- a/libavformat/movenc.c
+++ b/libavformat/movenc.c
@@ -3966,7 +3966,7 @@ static int mov_write_edts_tag(AVIOContext *pb, MOVMuxContext *mov,
     int flags = 0;
 
     if (track->entry) {
-        if (start_dts != track->cluster[0].dts || start_ct != track->cluster[0].cts) {
+        if (start_dts != track->cluster[0].dts || (start_ct != track->cluster[0].cts && track->cluster[0].dts >= 0)) {
 
             av_log(mov->fc, AV_LOG_DEBUG,
                    "EDTS using dts:%"PRId64" cts:%d instead of dts:%"PRId64" cts:%"PRId64" tid:%d\n",
@@ -6928,7 +6928,7 @@ int ff_mov_write_packet(AVFormatContext *s, AVPacket *pkt)
         trk->flags |= MOV_TRACK_CTTS;
     trk->cluster[trk->entry].cts   = pkt->pts - pkt->dts;
     trk->cluster[trk->entry].flags = 0;
-    if (trk->start_cts == AV_NOPTS_VALUE)
+    if (trk->start_cts == AV_NOPTS_VALUE || (pkt->dts <= 0 && trk->start_cts > pkt->pts - pkt->dts))
         trk->start_cts = pkt->pts - pkt->dts;
     if (trk->end_pts == AV_NOPTS_VALUE)
         trk->end_pts = trk->cluster[trk->entry].dts +
-- 
2.43.0


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